The present invention relates to a semiconductor structure applicable to semiconductor devices, such as MOSFET""s (insulated gate field effect transistors), IGBT""s (insulated gate bipolar transistors) and bipolar transistors. More specifically, the present invention relates to a bidirectional super-junction semiconductor device that exhibits a high breakdown voltage and a high current capacity and facilitates making a current flow from the first device region to the second device region and vice versa and a method of manufacturing the bidirectional super-junction semiconductor device.
The super-junction semiconductor device is a semiconductor device that includes a drift region including one or more alternating conductivity type layers. The alternating conductivity type layer provides a current path in the ON-state of the semiconductor device and is depleted in the OFF-state of the semiconductor device. The alternating conductivity type layer is formed of drift regions of a first conductivity type (e.g. an n-type) and partition regions of a second conductivity type (e.g. a p-type) arranged alternately.
FIG. 27 is a cross sectional view of a conventional vertical bidirectional MOS-type semiconductor device, disclosed in Japanese Unexamined Laid Open Patent Application H07-307469, that facilitates controlling a DC current and an AC current at a low on-voltage. Referring now to FIG. 27, the conventional bidirectional MOS-type semiconductor device includes a first n-channel IGBT and a second n-channel IGBT. The first n-channel IGBT is formed of n+-type emitter layers 102, p-type base layers 103, an nxe2x88x92-type substrate 101 and p-type anode layers 104. The second n-channel IGBT is formed of n+-type emitter layers 105, p-type base layers 104, an nxe2x88x92-type substrate 101 and p-type anode layers 103. The operation of the second n-channel IGBT is the inversion of the operation of the first n-channel IGBT. The first n-channel IGBT makes a current flow from a first terminal 106 to a second terminal 107. The second n-channel IGBT makes a current flow from second terminal 107 to first terminal 106.
In the conventional MOSFET""s, low on-resistance causes a low breakdown voltage and a high breakdown voltage causes high on-resistance. That is, a tradeoff relation exists between the on-resistance and the breakdown voltage. The tradeoff relation between the on-resistance and the breakdown voltage exists also in IGBT""S, bipolar transistors and diodes. The tradeoff relation exists in the vertical devices, in that the flow direction of the drift current and the expansion direction of the depletion layers coincide with each other, and in the lateral devices, in that the flow direction of the drift current and the expansion direction of the depletion layers are different from each other.
Japanese Unexamined Laid Open Patent Application H10-209267 discloses a super-junction semiconductor device that reduces the tradeoff relation described above. The disclosed super-junction semiconductor device includes a heavily doped alternating conductivity type drift layer formed of n-type regions and p-type regions arranged alternately. The alternating conductivity type layer is depleted to sustain a high breakdown voltage in the OFF-state of the device. Since the depletion layers that expand from the pn-junctions between n-type regions and the p-type regions in the OFF-state of the device deplete the entire drift layer, a high breakdown voltage is obtained even when the alternating conductivity type drift layer is doped heavily.
However, the super-junction MOSFET""s proposed so far are unidirectional devices, that are capable of controlling the current flowing from the drain to the source but incapable of controlling the current flowing from the source to the drain. In other words, any semiconductor structure, that facilitates reducing the tradeoff relation between the on-resistance and the breakdown voltage of the bidirectional semiconductor devices, has not been proposed so far. Although the super-junction semiconductor device structures proposed so far sustain the breakdown voltage when the drain is biased at a potential higher than the source potential, the super-junction semiconductor device structures proposed so far fail to sustain the breakdown voltage when the drain is biased at a potential lower than the source potential.
In view of the foregoing, it is an object of the invention to provide a bidirectional super-junction semiconductor device that exhibits a high breakdown voltage and facilitates making a current flow from the first device region to the second device region and vice versa across low on-resistance. It is another object of the invention to provide a method of manufacturing the bidirectional super-junction semiconductor device.
According to a first embodiment of the present invention, there is provided a bidirectional super-junction semiconductor device including: a semiconductor chip having a first major surface and a second major surface, the semiconductor chip including an alternating conductivity type layer between the first major surface and the second major surface; the alternating conductivity type layer being formed of drift regions of a first conductivity type and partition regions of a second conductivity type, the alternating conductivity type layer providing a current path in the ON-state of the semiconductor device, the alternating conductivity type layer being depleted in the OFF-state of the semiconductor device; a first device region on a first side of the alternating conductivity type layer; a second device region on a second side of the alternating conductivity type layer facing opposite to the first side; first regions of the second conductivity type in the first device region; second regions of the second conductivity type in the second device region; and a semiconductor region of the first conductivity type, the semiconductor region including at least the drift regions, the semiconductor region isolating the first regions and the second regions form each other, the semiconductor region isolating the partition regions from the first regions and the second regions.
Since the semiconductor region of the first conductivity type isolates the partition regions of the second conductivity type, the first regions of the second conductivity type in the first device region and the second regions of the second conductivity type in the second device region from each other, a high breakdown voltage is obtained in the opposite directions.
Advantageously, the semiconductor region of the first conductivity type includes a third region of the first conductivity type in the first device region and a fourth region of the first conductivity type in the second device region, and the third region and the fourth region are connected to each other via the drift regions. This configuration facilitates making a current flow from the first device region to the second device region and vice versa and reducing the on-resistance.
According to a second embodiment of the present invention, there is provided a bidirectional super-junction semiconductor device including: a semiconductor chip having a first major surface and a second major surface, the semiconductor chip including a first alternating conductivity type layer and a second alternating conductivity type layer between the first major surface and the second major surface; the first alternating conductivity type layer being formed of drift regions of a first conductivity type and partition regions of a second conductivity type, the first alternating conductivity type layer providing a current path in the ON-state of the semiconductor device, the first alternating conductivity type layer being depleted in the OFF-state of the semiconductor device; the second alternating conductivity type layer being formed of drift regions of the first conductivity type and partition regions of the second conductivity type, the second alternating conductivity type layer providing a current path in the ON-state of the semiconductor device, the second alternating conductivity type layer being depleted in the OFF-state of the semiconductor device; a first device region on a side of the first alternating conductivity type layer; a second device region on a side of the second alternating conductivity type layer; and a semiconductor region of the first conductivity type, the semiconductor region isolating the partition regions of the first alternating conductivity type layer and the partition regions of the second alternating conductivity type layer from each other.
The partition regions on the side of the first device region and the partition regions on the side of the second device region are isolated from each other by the semiconductor region of the first conductivity type. The first regions in the first device region and the second regions in the second device region are isolated from each other even when the partition regions in the first alternating conductivity type are connected to the first regions and the partition regions in the second alternating conductivity type are connected to the second regions. Therefore, a high breakdown voltage is obtained in the opposite directions between the first device region and the second device region.
In the configurations described above, the drift regions in the first alternating conductivity type layer and the drift regions in the second alternating conductivity type layer may be connected via the semiconductor region of the first conductivity type. Since a current path is formed by connecting the drift regions in the first alternating conductivity type layer and the drift regions in the second alternating conductivity type layer, a current is made flow from the first device region to the second device region and vice versa, and the on-resistance is reduced.
According to a third embodiment of the invention, there is provided a method of manufacturing a bidirectional super-junction semiconductor device formed of a first half device and a second half device; the first half device including a first device region and a first alternating conductivity type layer formed of drift regions of a first conductivity type and partition regions of a second conductivity type, the first alternating conductivity type layer providing a current path in the ON-state of the semiconductor device, the first alternating conductivity type layer being depleted in the OFF-state of the semiconductor device; the second half device including a second device region and a second alternating conductivity type layer formed of drift regions of the first conductivity type and partition regions of the second conductivity type, the second alternating conductivity type layer providing a current path in the ON-state of the semiconductor device, the second alternating conductivity type layer being depleted in the OFF-state of the semiconductor device, the method including the steps of: forming the first half device; forming the second half device; and bonding the back surface of the first half device, under that the first device region is not formed, and the back surface of the second half device, under that the second device region is not formed. Since the first alternating conductivity type layer and the second alternating conductivity type layer are formed easily by the manufacturing method described above, the manufacturing process is simplified and the manufacturing costs are reduced.